/*
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at 
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */
using System;

namespace org.apache.commons.pool
{

    /**
     * An interface defining life-cycle methods for
     * instances to be served by an {@link ObjectPool}.
     * <p>
     * By contract, when an {@link ObjectPool}
     * delegates to a {@link PoolableObjectFactory},
     * <ol>
     *  <li>
     *   {@link #makeObject makeObject}
     *   is called whenever a new instance is needed.
     *  </li>
     *  <li>
     *   {@link #activateObject activateObject}
     *   is invoked on every instance that has been
     *   {@link #passivateObject passivated} before it is
     *   {@link ObjectPool#borrowObject borrowed} from the pool.
     *  </li>
     *  <li>
     *   {@link #validateObject validateObject}
     *   is invoked on {@link #activateObject activated} instances to make sure
     *   they can be {@link ObjectPool#borrowObject borrowed} from the pool.
     *   <code>validateObject</code> <strong>may</strong> also be used to test an
     *   instance being {@link ObjectPool#returnObject returned} to the pool
     *   before it is {@link #passivateObject passivated}. It will only be invoked
     *   on an activated instance.
     *  </li>
     *  <li>
     *   {@link #passivateObject passivateObject}
     *   is invoked on every instance when it is returned to the pool.
     *  </li>
     *  <li>
     *   {@link #destroyObject destroyObject}
     *   is invoked on every instance when it is being "dropped" from the
     *   pool (whether due to the response from <code>validateObject</code>,
     *   or for reasons specific to the pool implementation.) There is no
     *   guarantee that the instance being destroyed will
     *   be considered active, passive or in a generally consistent state.
     *  </li>
     * </ol>
     * </p>
     * <p>
     * {@link PoolableObjectFactory} must be thread-safe. The only promise
     * an {@link ObjectPool} makes is that the same instance of an object will not
     * be passed to more than one method of a <code>PoolableObjectFactory</code>
     * at a time.
     * </p>
     *
     * @param <T> the type of objects held in this pool
     * 
     * @see ObjectPool
     *
     * @author Rodney Waldhoff
     * @author Sandy McArthur
     * @version $Revision: 1222388 $ $Date: 2011-12-22 13:28:27 -0500 (Thu, 22 Dec 2011) $
     * @since Pool 1.0
     */
    public interface PoolableObjectFactory<T>
    {
        /**
         * Creates an instance that can be served by the pool.
         * Instances returned from this method should be in the
         * same state as if they had been
         * {@link #activateObject activated}. They will not be
         * activated before being served by the pool.
         *
         * @return an instance that can be served by the pool.
         * @throws Exception if there is a problem creating a new instance,
         *    this will be propagated to the code requesting an object.
         */
        T makeObject();// throws Exception;

        /**
         * Destroys an instance no longer needed by the pool.
         * <p>
         * It is usingant for implementations of this method to be aware
         * that there is no guarantee about what state <code>obj</code>
         * will be in and the implementation should be prepared to handle
         * unexpected errors.
         * </p>
         * <p>
         * Also, an implementation must take in to consideration that
         * instances lost to the garbage collector may never be destroyed.
         * </p>
         *
         * @param obj the instance to be destroyed
         * @throws Exception should be avoided as it may be swallowed by
         *    the pool implementation.
         * @see #validateObject
         * @see ObjectPool#invalidateObject
         */
        void destroyObject(T obj);// throws Exception;

        /**
         * Ensures that the instance is safe to be returned by the pool.
         * Returns <code>false</code> if <code>obj</code> should be destroyed.
         *
         * @param obj the instance to be validated
         * @return <code>false</code> if <code>obj</code> is not valid and should
         *         be dropped from the pool, <code>true</code> otherwise.
         */
        bool validateObject(T obj);

        /**
         * Reinitialize an instance to be returned by the pool.
         *
         * @param obj the instance to be activated
         * @throws Exception if there is a problem activating <code>obj</code>,
         *    this exception may be swallowed by the pool.
         * @see #destroyObject
         */
        void activateObject(T obj);// throws Exception;

        /**
         * Uninitialize an instance to be returned to the idle object pool.
         *
         * @param obj the instance to be passivated
         * @throws Exception if there is a problem passivating <code>obj</code>,
         *    this exception may be swallowed by the pool.
         * @see #destroyObject
         */
        void passivateObject(T obj);// throws Exception;
    }
}